OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 2 2022 of aluminum alloys forming process it becomes possible to conduct the deformation process at moderate temperatures in contrast, for example, to the copper or steel forming. As a result, the tooling retains the strength properties, even if it is heated to the deformation point. This brings the process to the isothermal treatment level, which should stabilize the fi nal product properties. At the same time, extrusion is characterized by increased metal waste in the form of cutoff front and rear parts. It is rejected due to a different deformed condition than the product main part [3]. For example, the rear pressed profi le part is characterized by the funnel formation and, as a result, the product is prone to defect [4, 5]. The profi le front part is characterized by a low strain degree, which leads to an elaboration lack in the cast metal structure. As a result, the mechanical properties in this place are low and does not correspond the standard requirements. In addition, standards, especially for products made of aluminum alloys for aviation purposes, dictate the requirements for the structural state of the metal, and it may also not be met. The inhomogeneity of the structure and properties of the extruded semi-fabricated products along the length and cross section is the subject of study of the technological services of enterprises and research institutions [6, 7]. The extruded product front part occurs under low plastic deformation conditions. If extrusion process is planned with pre-reduced elongation ratio, then the effect of these two phenomena is summed up and its consequences should be considered. The extrusion process with low elongation ratio was analyzed, for example, by the authors [8] for the aluminum alloy extrusion case. The elongation ratio may be reducing due to the use of ingots with smaller cross-sections. The energy input is reduced since this reduces the plastic deformation level. But at the same time, the issue of bringing plastic deformation to such values remains relevant so that the necessary product properties are obtained. There is a problem of achieving the optimal strain amount, which minimizes energy costs and improves product quality. As a result, technical solutions began to appear to increase the strain during pressing, at least magnesium alloys [9]. Another reason for the poor properties of the front parts of the press products is its cracking after leaving the die. The fact is that the stressed state of the metal near the die differs from the state of the metal in the container of the press. In the latter case, it is a stressed state of all-round compression [10], which increases the plasticity of the metal. However, the metal near the opening of the die has a free surface without forces counteraction. The ductility is reduced for insuffi ciently plastic aluminum alloys since the metal ductility is a stress state function in the absence compression stresses. It is possible that fl aw may appear on the press product front part leaving the extrusion die, which is shown in [11] on the example of large-sized pipes production. Upon transition to the stationary stage of extrusion, the effect of the absence of the front forces counteraction disappears, and the product ceases to destruction. Therefore, the determination of the deformed state of the front part of the pressed product, especially in conditions of deformation with low elongation ratio, is an urgent task. Physical modeling can be used to analyze the stress-strain state during extrusion [12], but recently the fi nite element method implemented in various software products has been most often used: QFORM [13, 14], FORGE [15], DEFORM [16-18], RAPID [19] et al. This makes it possible to evaluate the situation at each elementary point of the deformable metal. At the same time, it is possible to consider a variety of the deformable materials properties and boundary conditions in production situations. The work aim is to establish the extruded rod front part strain inhomogeneity level by numerical simulation using the fi nite element method. Research methodology The direct extrusion process is carried out by pushing the ingot metal 1, located in the container 2, by the hob force 3 through the extrusion die hole 4 (Fig. 1). As a result, the rod front part 5 fi rst extruded die hole, then a process stationary stage occurs, and the entire ingot is extruded with the extrusion discard exception.
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